1. Field of the Invention
The present invention relates to machines that grind saw blades, and more particularly to such machines that automatically grind the top and face of each tooth of a circular saw blade.
2. Description of the Related Art
Circular saw blades are conventionally ground by systems including various types of circular grinding wheels to grind the saw blade teeth. The critical parameter in grinding a saw blade is "precise replication." All of the saw teeth in a given saw blade must be precisely ground to a similar configuration which is uniform within extremely narrow tolerances.
Various automatic machines for grinding saw blades have been proposed for the purpose of precise grinding replication results. One such automatic machine is disclosed in U.S. Pat. No. 4,750,387 to Swiger, assigned to Cascade/Southern Saw Corp. This patent discloses a saw grinding machine for grinding the sides of teeth, not the top and face of the teeth, but it shares many of the same problems as a top and face grinder.
Top and face grinding machines employ automatic indexers to advance the circular saw blade a predetermined distance to grind each tooth in turn. Such indexers have to adapt to a plurality of saw blades having widely varying tooth spacings and diameters. As a saw blade is rotated, a tooth on the outside radius of a large diameter saw blade travels along a different arcuate path than does a tooth on a small diameter saw blade. Ideally, the part of an indexer that engages the tooth on a saw blade, i.e., a pawl, should advance along the same circumferential path as the tooth. Thus, an indexer must be adaptable to accommodate a different path for each circular saw blade having a different diameter, as well as a different path length for blades of different diameters and tooth spacings.
Saw sharpening machines known in the prior art automatically index circular saw blade teeth. Indexers employed in such machines, however, have serious drawbacks. For example, in the Vollmer Werke Maschinenfabrick GmbH (Vollmer) commercial top and face circular saw grinder, Model CHC, the indexer is hydraulically operated with one hydraulic drive that reciprocally moves a pawl from a first retracted position to a second extended position. The indexer is pivotally mounted so that the pawl travels in an arcuate path responsive to a cam follower that moves relative to a cam surface. A feed curve inset block providing a specific cam surface is employed in conjunction with a saw blade having a specific diameter. This system is effective, but when a saw blade of different diameter is to be ground, a different feed curve inset block suited for that specific diameter must be installed. Installing a different cam for each change to a saw blade having a different diameter requires time and labor of an operator. The machine must be shut down during this change of cams, so the system is very inefficient.
In view of the foregoing problem, other solutions to indexing circular saw blades have been proposed. One such solution is disclosed in U.S. Pat. No. 4,488,458 to Beck, assigned to Vollmer. The Beck indexer requires the coordination of two complex mechanical systems to achieve the desired results of having a pawl move in an arcuate path defined by a tooth on a rotating circular saw. Beck employs two controllable linear drive means: one drive means pivots the indexer while the other extends the pawl. Because Beck requires two drive means that must simultaneously work in unison, however, it is unnecessarily complex in its design and control. This, in turn, creates problems with precise alignment and precise replication as well as problems with maintenance.
Beyond the problems noted above, to be fully useful, automatic top and face grinding machines must be able to grind the face of saw teeth having either positive or negative rake angle. Although some grinding machines are so designed, they generally require the operator to reconfigure the machine to change from a positive to a negative rake angle or vice versa. One such grinder is disclosed in U.S. Pat. No. 4,136,585 to Lenard, assigned to Vollmer. Lenard discloses an automatic grinding machine with a carrier that tilts about an axis perpendicular to the plane of a saw blade. The carrier supports a carriage that swivels 180.degree. so that the grinding surface of a grinding wheel mounted thereto can be positioned for either a positive or negative rake angle. The problem with this arrangement, however, is that changing the setting of the machine from positive to negative rake angle, or vice versa, is inefficient. An operator must first tilt the carrier, then he must swivel the carriage 180.degree. , and finally he must invert the grinding wheel over so that the angled grinding surface is properly facing the saw tooth. These steps are labor intensive and require the grinding machine to be shut down for a considerable period.
In addition to the foregoing, during operation of the Lenard top and face grinder adverse vibrations are generated. We believe the vibrations arise because the carrier cantilevers from the tilting axis and because the motor that drives the grinding wheel is disposed at the farthest point from the tilting axis. Such vibrations have a detrimental effect on the precise replication required for grinding circular saw blades.
Therefore, there is a need for an improved top and face grinder that exhibits a high degree of flexibility and precise replication not achievable using conventional automatic top and face grinders.